Why Naughty Boy
is a giant leap.

After a 27.5 hour countdown, the three stage rocket left the Second Launch Pad about 135 km east of Chennai despite heavy rain. Mission Director Thomas Kurian cleared the automated sequence once telemetry and control were healthy. Chairman V Narayanan called it a perfect launch. The cryogenic upper stage delivered roughly 1,000 km more apogee than the planned 29,934 km, leaving extra fuel on EOS-05 for the climb to the geo platform.

Friday’s flight was ISRO’s first successful orbital launch of 2026. The year’s earlier attempt, PSLV-C62 with EOS-N1 on 12 January, failed near the end of third stage flight. GSLV-F17 closed an eight month gap and put the agency back on a demanding calendar that still includes NVS-03 and the first uncrewed Gaganyaan test.

The Geosynchronous Satellite Launch Vehicle was built to loft about two tonne class satellites toward geostationary transfer orbits. It is heavier than PSLV, with a cryogenic upper stage that India had to invent after 1990s technology control limits blocked a full cryogenic transfer from Russia. Early flights were unforgiving. From the first development launch in April 2001 through 2014, only two of seven missions fully succeeded. Inside ISRO the rocket picked up a nickname: Naughty Boy.

After GSAT-14 reached orbit in 2014, then project director K. Sivan said the naughty boy had become obedient. The remaining weak point was still the indigenous cryogenic upper stage. On 12 August 2021, GSLV-F10 carried GISAT-1 (EOS-03). The first two stages flew cleanly. The cryogenic stage did not ignite. India lost its first geo imaging satellite.

“We used to call GSLV the naughty boy of ISRO. The naughty boy has become obedient.”

K. Sivan after GSAT-14, 2014

F17 is the 19th GSLV flight and the first GSLV mission since F16 lofted the NASA ISRO NISAR radar satellite into sun synchronous orbit on 30 July 2025. The CUS15 stage is white, better insulated and lighter, flying the CE-7.5 engine on liquid hydrogen and liquid oxygen. That is the machine that had to work this morning. It did, and then some.

EOS-05, also reported as GISAT-1A, is the second spacecraft in ISRO’s Geo Imaging Satellite series and the replacement for the lost GISAT-1 / EOS-03. It is built around a modified I-2K bus with a 700 mm Ritchey Chrétien telescope derived from Cartosat-2A thinking: a jitter quiet platform, electronically steerable phased array downlink, and array detectors in visible, near infrared and short wave infrared.

Most of India’s 21 operational Earth observation satellites (as of February 2026) live in low Earth orbit or sun synchronous polar orbits. Geostationary Earth observation until now meant weather birds such as INSAT-3D, 3DR and 3DS. EOS-05 is the first Indian satellite designed to take dedicated multi spectral and hyperspectral images from a geosynchronous vantage, about 36,000 km up. Union minister Jitendra Singh noted imaging across visible, infrared, multi spectral and hyperspectral bands.

Injection was into a sub geosynchronous transfer orbit, not the final workplace. A sub GTO trades a lower apogee than classical GTO so the launcher can lift more mass. The satellite then spends days raising itself with onboard propulsion. Narayanan said teams will raise the orbit and take it to the required orbit and place the satellite in the geo platform. Extra apogee at injection means less of that propellant is burned just to catch up. More life, more pointing, more pictures.

From geosynchronous altitude a spacecraft can remain over the same longitude, looking down on India, the Himalaya, the Indian Ocean approaches and neighbouring regions in one long take. GISAT literature describes a selected field image every five minutes and a full landmass product every half hour at 42 m in MX VNIR, always with the caveat of cloud free lines of sight.

Three stories landed at once. First, India finally owns the geo imaging gap it tried to close in 2020 and 2021: continuous Earth observation from 36,000 km, not another low orbit snapshot. Second, GSLV Mk II has now lofted its heaviest satellite and flown a cryogenic stage that beat the book. That is a reliability signal for every future GSAT, navigation spare and science payload that still needs this rocket. Third, ISRO is flying again after a failed year opener, with Gaganyaan’s first uncrewed mission still on the 2026 board.

EOS-05 is not yet on station. Commissioning, orbit raising and geo platform capture still have to succeed. When they do, India will have a staring eye that weather satellites cannot match in spectral richness and that low orbit imagers cannot match in persistence. That is the leap. Not a bigger bang on the pad, but a new way of seeing the country in near real time.

“The satellite will continuously scan India for safety, security of citizens, it’s not a spy satellite.”

V Narayanan, Chairman, ISRO, 4 September 2026